FIG. 1 is a schematic showing a perspective cross sectional view of a conventional silicon microphone 100. In some conventional silicon microphone micro-electromechanical system (MEMS) chips 100, the active areas includes a very thin membrane 102, typically having a thickness of a few hundred nanometers as well as a counter electrode 104 suspended over a through hole 106. The micro-electromechanical system (MEMS) chip 100 with the membrane 102 is etched from the backside. The counter electrode 104 is also typically very thin. Both the membrane 102 and the counter electrode 104 are partially metalized. Acoustic waves will impinge on the membrane 102. This will cause the membrane 102 to oscillate. The acoustic waves are detected by measuring the capacitance change due to the oscillation of the membrane 102. The performance of the microphone usually depends on the volume on the back side of the membrane, i.e. the side opposite the front side in which acoustic wave impinge on.
FIG. 2 is a diagram showing various components that may be present in a conventional silicon microphone 200. The silicon microphone includes a micro-electromechanical system (MEMS) chip 202 with a membrane 204. The MEMS chip 202 is mounted and wire bonded to a substrate 206. The silicon microphone 200 may also include an optional logic chip 208. The micro-electromechanical chip 202 and the optional logic chip 208 may be connected by electrical leads. The silicon microphone 200 also has a lid 210 to cover the micro-electromechanical chip 202 and the optional logic chip 208.
FIG. 3 is a schematic showing a side cross sectional view of another conventional silicon microphone 300. A micro-electromechanical system (MEMS) chip 302 is mounted on a substrate 304. An application specific integrated circuit (ASIC) chip 306 is also mounted onto the substrate 304. The ASIC chip 306 is wire bonded to the MEMS chip 302. The ASIC chip 306 is also wire bonded to the substrate 304. An electrically conductive lid 308 is used to cover the MEMS chip 302 and the ASIC chip 306. The lid 308 has an opening or hole 310 which allows the input or entry of sound such that acoustic waves is able to reach the MEMS chip 302. The volume below the MEMS chip 302 that is being removed by means of etching is the backside volume. The lid 308 may be used as a shielding from electromagnetic waves and therefore is electrically connected to the substrate 304. The ASIC chip 306 is usually covered with a polymer for reliability reasons (such as protecting exposed aluminum metallization form corrosion).
The manufacture of conventional silicon microphones typically involves numerous processing steps and/or require the use of complicated machines. It is also difficult to adjust the backside volume to optimize the performance of the silicon microphones as the backside volume is limited by the thickness of the wafer in which the MEMS chip is fabricated from.